1. Field of the Invention
In one of its aspects, the present invention relates to an optical radiation sensor system. In another of its aspects, the present invention relates to a method for measuring radiation transmittance of a fluid.
2. Description of the Prior Art
Optical radiation sensors are known and find widespread use in a number of applications. One of the principal applications of optical radiation sensors is in the field of ultraviolet radiation fluid disinfection systems.
It is known that the irradiation of water with ultraviolet light will disinfect the water by inactivation of microorganisms in the water, provided the irradiance and exposure duration are above a minimum “dose” level (often measured in units of milliWatt seconds per square centimetre or mW*s/cm2). Ultraviolet water disinfection units such as those commercially available from Trojan Technologies Inc. under the tradenames Trojan UVMax™, Trojan UVSwift™ and Trojan UVLogic™, employ this principle to disinfect water for human consumption. Generally, water to be disinfected passes through a pressurized stainless steel cylinder which is flooded with ultraviolet radiation. Large scale municipal waste water treatment equipment such as that commercially available from Trojan Technologies Inc. under the tradenames UV3000 and UV4000, employ the same principle to disinfect waste water. Generally, the practical applications of these treatment systems relates to submersion of a treatment module or system in an open channel wherein the wastewater is exposed to radiation as it flows past the lamps. For further discussion of fluid disinfection systems employing ultraviolet radiation, see any one of the following:
a. U.S. Pat. No. 4,482,809,
b. U.S. Pat. No. 4,872,980,
c. U.S. Pat. No. 5,006,244,
d. U.S. Pat. No. 5,418,370,
e. U.S. Pat. No. 5,504,335
f. U.S. Pat. No. 5,539,210, and
g. U.S. Pat. Re36,896.
In many applications, it is desirable to monitor the level of ultraviolet radiation present within the water (or other fluid) under treatment or other investigation. In this way, it is possible to assess, on a continuous or semi-continuous basis, the level of ultraviolet radiation, and thus the overall effectiveness and efficiency of the disinfection process.
It is known in the art to monitor the ultraviolet radiation level by deploying one or more passive sensor devices near the operating lamps in specific locations and orientations which are remote from the operating lamps. These passive sensor devices may be photodiodes, photoresistors or other devices that respond to the impingement of the particular radiation wavelength or range of radiation wavelengths of interest by producing a repeatable signal level (e.g., in volts or amperes) on output leads.
In most commercial ultraviolet water disinfection systems, the single largest operating cost relates to the cost of electricity to power the ultraviolet radiation lamps. In a case where the transmittance of the fluid varies from time to time, it would be very desirable to have a convenient means by which fluid transmittance could be measured for the fluid being treated by the system (or the fluid being otherwise investigated) at a given time. If it is found that fluid transmittance is relatively high, it might be possible to reduce power consumption in the lamps by reducing the output thereof. In this way, the significant savings in power costs would be possible.
The measurement of fluid transmittance is desirable since measurement of intensity alone is not sufficient to characterize the entire radiation field—i.e., it is not possible to separate the linear effects of lamp aging and fouling from exponential effects of transmittance. Further, dose delivery is a function of the entire radiation field, since not all fluid takes the same path.
The prior art has endeavoured to develop reliable radiation (particularly UV) transmittance measuring devices.
For example, it is known to use a single measurement approach. Unfortunately, the single measurement distance requires re-calibration with fluid of known transmittance to account for fouling.
It is also known to use a two-sensor system in which a first sensor is disposed in air and a second sensor is disposed in water. The problem with this approach is that it results in different fouling of each sensor with resulting errors.
Further, some systems require obtaining a sample from a channel of flowing fluid and thereafter measuring the radiation transmittance of the sample. Unfortunately, this approach necessitates the use of additional fluid handling measures which can lead to non-representative samples.
International Publication Number WO 01/96823 and published United States patent application 2002/0036274 [both in the name of Ellis et al. (Ellis) and assigned to the assignee of the present invention] teach an optical radiation sensor device for detecting radiation in a radiation field. A preferred embodiment of the device includes a radiation source and a radiation sensor element positioned to receive radiation from the radiation source. A motor (or other motive means) is provided to alter the thickness of the radiation field from a first thickness to a second thickness. The sensor element is capable of detecting and responding to incident radiation from a radiation source at the first thickness and at the second thickness. The optical radiation sensor device allows for determination of radiation (preferably ultraviolet radiation) transmittance of a fluid of interest.
Conventionally, radiation (e.g., ultraviolet radiation) transmittance of a fluid has been done by utilizing a monochromatic radiation—i.e., a radiation source that will emit a single wavelength of interest, so that the sensor element is used in a manner whereby a single wavelength of interest is detected and processed.
A problem with this conventional approach is that there can be significant errors in radiation transmittance calculated using the monochromatic measurement technique on a given fluid flow due to variation in radiation transmittance with the wavelength of the light that is detected and processed.
Thus, despite the advances made in the art, there exists a need for an improved device which can measure radiation transmittance of a fluid. Ideally, the device would be to respond to polychromatic radiation and measure UV transmittance of a fluid in an on-line or random measurement manner.